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A new study finds that the mystery behind why Venus’s atmosphere spins much faster than the planet’s surface can finally be solved.
The finding could help shed light on how habitable distant exoplanets, or worlds beyond our solar system, may be, according to the researchers.
Related: The 10 strangest facts about Venus
This mysterious phenomenon of atmospheric super rotation is seen not only on Venus, but also on Saturn’s largest moon, Titan. Previous research suggested that for this super rotation to occur, the atmosphere of Venus must possess enough angular momentum, the amount of momentum a body has due to its rotation, to overcome friction with the planet’s surface. However, it was unclear exactly what the source of this angular momentum was.
To shed light on this mystery, the scientists analyzed data from the Japanese space probe Akatsuki, which has orbited Venus since 2015. They focused on super rotation in the Venus cloud layer, where the speed of rotation is highest, reaching approximately 245 mph (395 mph). km / h) in the region around the equator.
Based on Akatsuki’s ultraviolet images and thermal infrared data, the scientists developed a way to track the movements of Venus’ clouds to map the planet’s winds and how heat circulated in the atmosphere. This helped give researchers a picture of how the angular momentum was distributed at the cloud’s upper level, located at approximately 42 miles (70 kilometers) altitude. This in turn helped them estimate the forces holding the super-spinning atmosphere.
“Personally, our success in doing so was my biggest surprise,” study lead author Takeshi Horinouchi, a planetary scientist at Hokkaido University in Sapporo, Japan, told Space.com.
Scientists discovered that the Venusian atmosphere received an angular boost through thermal tides, which are variations in atmospheric pressure driven by solar warming near the planet’s equator. They also found planetary-scale waves in the atmosphere, as well as large-scale atmospheric turbulence against this effect of thermal tides.
“There was a suggestion that the thermal tides could be contributing to the acceleration behind the super rotation, but I think the main assumption was different, so it was a surprise,” Horinouchi said.
These findings can shed light on the habitability of exoplanets blocked by the tide, worlds in which each has a dark side that is always away from its star and a side that is bathed in constant sunlight. One might expect that the sides of these exoplanets were hot and the night sides were cold, and that conditions for life, as we know, could be more favorable in the twilight zone between these sides. However, super rotation could balance temperature differences between days and nights, Horinouchi said.
Future research may investigate how atmospheric super rotation on Venus has remained stable over time, Horinouchi said.
The scientists detailed their findings in the April 24 issue of the journal Science.
Follow Charles Q. Choi on Twitter @cqchoi. Follow us on twitter @Spacedotcom and in Facebook.
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